268 
ZOOLOGICAL LITERATURE. 
poda of a new species of Orchestia^ O. tucuratinga, and slightly 
alludes to the development of the Diastylidse, which was first 
shown by Mr. Spence Bate, and not, as he states, by Prof.Kroyer. 
IX. Dr. Miiller here describes the development of Branchio- 
poda, Copepoda, Osti'acoda, Cirripedia, Sacculina, &c., or those 
Crustacea which liave the larva in the Nauplius form. He alludes 
to the close resemblance between the development of the Cir- 
ripedia and Sacculina, not only in the larval but in the pupa stage, 
the divergence of the two commencing from the period when 
these mouthless animals attach themselves to their future rest- 
ing-place — the one building with a cement-organ a stalk on 
which to rest, the other sending deep fibres into the animal on 
which it has fastened. One great dilference now exists : the 
cirripede ceases to be mouthless, and strikes out its limbs for 
food; the Sacculina remains mouthless, and vegetates into a 
sac that fills with eggs. He likewise speaks of the early division 
of the yelk in the ovum, &c. 
X. Dr. Muller combats the opinions of Agassiz and J. Miillex’, 
who, with others, have announced that in the development of an 
animal the changes in form are in proportion to the variation 
of the species from the type of the family to which it belongs. 
He also disputes — and successfully, we think — the assertion 
of Agassiz, that the egg-material of all animals is perfectly 
identicaP^*, by showing that in Crustacea the egg-material pre- 
sents excellent marks for distinguishing the species of the same 
genus : in a certain Porcellana the ova are dark green, in a 
second dark blood-red, in a third gold-yellow. He denies, 
further, the truth of the statement that ^‘^the organs of the 
body are formed in the order of their relative importance, the 
most essential always appearing the first — that is to say, that 
the physiological and systematic value do not coincide — illus- 
trating his opinion by numerous examples of unimportant organs 
appearing before others more essentia;! to the existence of animal 
life, and arrives at the conclusion that a classification of a group 
of animals can only be natural when its genera ai’e arranged in 
accordance with their agreement with the succession of the 
organs in the development of the embryo,^^ and that a true and 
natural system of Crustacea must be based on the following 
successive changes : — 
First, the different modes of the division of the yelk ; 
Second, the settling of the embryo ; 
* Principles of Zoology, part I. Commrative Physiology.” By Louis 
Agassiz and A. A. Gould. Third edit. Boston, 1856. We have not the 
American edition by us to refer to, nor can we find the passage as quoted by 
Dr. Muller in the English edition of 1851 ; but at p. 273, pax’agraph 436, speak- 
ing of ovarian or primitive eggs, the authors say, “ They are identical in all 
animals, being, in fact, merely little cells containing yelk substance, including 
other similar cells, namely the germinative vesicle and germinative dot.” 
t Loc, cil. p. 278. 
